1. Field of the Invention
The present invention pertains to a method for the simultaneous removal of an oxygen and/or nitrogen-containing dielectric antireflective coating (xe2x80x9cDARCxe2x80x9d) during plasma etching of an underlying layer in a film stack.
2. Brief Description of the Background Art
In the field of semiconductor device fabrication, photoresists have been developed which are responsive to shorter wavelengths within the electromagnetic spectrum to enable the patterning of small-dimensioned electronic and optical devices. An example of one such class of photoresists are the deep ultraviolet photoresists (xe2x80x9cDUVxe2x80x9d), which are responsive to the shorter wavelengths in the ultraviolet region of the electromagnetic spectrum to pattern small dimensioned electronic and optical devices. The dimensions patterned with DUV photoresist are significantly smaller than device dimensions patterned using traditional or I-line photoresists.
Generally, a photoresist is used to provide a pattern on the surface of a stack of layers that are to be patterned in subsequent processing steps. The photoresist and some of the layers in the stack may be consumed in part or in whole during the process of patterning underlying layers which become part of the functioning device.
To take advantage of the spacial resolution capability available through ultraviolet wavelength imaging techniques, it is necessary to use an antireflective coating (xe2x80x9cARCxe2x80x9d) layer underneath the photoresist layer. The ARC layer provides several advantages to the fabrication process. First, the ARC layer tends to planarize the stack surface. Second, the ARC layer cuts down on light scattering from the surface into a DUV photoresist. The attenuation in light scattering from the surface the ARC layer aids in the definition of small images. Finally, the ARC layer minimizes standing wave effects and improves image contrast. Thus, the ultimate result of the ARC layer is to enable an accurate pattern replication.
Recently, there has been increased interest in the use of silicon oxynitride as an anti-reflective coating due to its ability to function well in combination with DUV photoresist. Silicon oxynitride typically (but not by way of limitation) has a formula of SiOxNy, where x ranges from about 0 to about 2, and y ranges from about 0 to about 1.33. By changing the composition of the silicon oxynitride ARC layer, one can control the refractive index (n) and the extinction coefficient (k) of the ARC layer. The refractive index and extinction coefficient, in combination with the thickness of the ARC layer, control reflection into the photoresist during imaging of the photoresist layer.
Use of silicon oxynitride as an ARC enables efficient suppression of the reflection from underlying layers while providing superior chemical properties. Silicon oxynitride""s chemical properties prevent photoresist poisoning. Photoresist poisoning occurs when the surface underlying the photoresist reacts with moisture, thereby forming anionic basic groups (NH2) which react with the photogenerated acid that is responsible for the development of the photoresist.
However, despite the advantages of ARC usage described above, when an ARC layer (such as silicon oxynitride) acts as a dielectric, residual ARC layer presence in an etched film stack (and ultimately within the device) may affect the performance of the device. In such instances, the entire dielectric ARC (DARC) layer should be removed, so that no residual DARC layer is present to interfere with device performance. Currently, an additional step must be performed in order to remove the residual DARC layer. This additional processing step increases production throughput time and cost. Therefore, finding a means to perform removal of the DARC layer during the plasma etching of an underlying etch stack layer would be advantageous.
The present invention provides a method which allows the simultaneous removal of an oxygen and/or nitrogen-comprising DARC layer during plasma etching of an underlying etch stack layer, using a plasma containing reactive fluorine species. We have observed that the use of a plasma source gas containing an inorganic fluorine-comprising compound, such as CF4, SF6, or NF3, permits the simultaneous removal of a DARC layer during a polycide, metal, or polysilicon gate etch step. One of the preferred embodiment DARCs is silicon oxynitride.
We have discovered preferred combinations of plasma source gases which provide for the simultaneous removal of an oxygen and/or nitrogen-containing DARC layer during etching of an underlying etch stack layer, where the underlying stack layer comprises a metal silicide, polysilicon, or a metal. Frequently, the plasma source gas includes chlorine and HBr as well as a source of fluorine species, because of the ability of chlorine and bromine, once energized, to etch the underlying etch stack layer. Increasing the ratio of fluorine to chlorine and/or bromine in the plasma source gas typically increases the etch rate of the DARC relative to the etch rate of the underlying etch stack layer. Additionally, an increase in the substrate bias voltage will typically increase the etch rate of the DARC relative to the etch rate of an underlying etch stack layer. Further, decreasing the oxygen and/or nitrogen content of the DARC layer will also typically tend to increase the etch rate of the DARC layer relative to the underlying etch stack layer.
In addition, we have developed a method useful in semiconductor processing for determining etch process conditions which provide for simultaneous removal of essentially all residue of an oxygen-containing antireflective coating layer during pattern etching of at least one underlying layer in a film stack, wherein said film stack comprises said oxygen-containing antireflective coating layer residue, said at least one underlying layer to be etched, and at least one hard mask layer beneath said underlying layer to be etched. The method includes a number of steps:
1) performing a series of experiments necessary to establish at least one analytical function, Sel=f (X flow rate),
where X represents a fluorine-comprising feed gas used to create an etch plasma,
where Selmin=dunderlying layer/(dantireflective coating layer+dhard mask layer),
where Selmax=dunderlying layer/dantireflective coating layers,
where dunderlayer=thickness of the underlying layer,
where dantireflective coating layer=thickness of the antireflective coating layer,
and where dhard mack layer=thickness of the hard mask layer;
2) selecting X flow rate so that Selmax is greater than Sel (X flow rate), which is greater than Selmin;
3) etching a pattern into the at least one underlying layer to be etched and determining:
a) is essentially all of the residue of said oxygen-containing antireflective coating layer removed during etching, and if it is not, increasing X flow rate,
b) is the hardmask layer sufficiently intact to be functional, and if it is not, decreasing X flow rate,
c) does a profile of the pattern etched into the underlying layer meet a predetermined requirement, and if it does not, adjusting at least one process variable selected from the group consisting of source power, bias power, and process chamber pressure; and
4) repeating step 3) until essentially all of the residue of the oxygen-containing antireflective coating layer is removed, said hard mask layer is sufficiently intact to be functional, and said profile of the pattern meets said predetermined requirement.
In one embodiment, the hard mask layer is an oxide-comprising layer.